The present invention relates to a hydraulic engagement apparatus for automatic transmissions.
The hydraulic engagement apparatus arranged in a power transmission serves as a shift element put in engagement or disengagement hydraulically. Conventionally, the hydraulic engagement apparatus comprises a reverse clutch for reverse run interposed between a reverse-clutch drum and a reverse-clutch hub and is put in engagement through a reverse-clutch piston, and a high clutch for overdrive interposed between a high-clutch drum and a high-clutch hub and is put in engagement through a high-clutch piston.
The reverse-clutch hub is fixed to the high-clutch drum, which is directly connected to an input shaft, and the reverse-clutch drum is connected to a sun gear of a front planetary gear, and the high-clutch hub is connected to a pinion carrier of the front planetary gear.
However, the known hydraulic engagement apparatus has the following problems:
1) Due to the structure with two clutch drums and two clutch hubs, the apparatus is large in size in the axial and radial directions, having a disadvantage in weight and space; PA1 2) Due to no existence of a rotary member, which rotates in the same way as the input shaft at the outer side of the apparatus, it is difficult to arrange a turbine sensor for measuring the turbine revolution available to shift control; and PA1 3) When racing the engine at N range with the high clutch seizing, the sun-gear connected members such as reverse-clutch drum and reverse-clutch piston are over-rotated, increasing possible burst of the reverse-clutch drum. That is, with the high clutch seizing, rotation of the input shaft is transmitted to the high-clutch hub through the high clutch, rotating the pinion carrier of the front planetary gear. This produces rotation of the sun gear with the input shaft rotating at increased speed, over-rotating the reverse-clutch drum, etc. connected to the sun gear. PA1 1) Since the reverse-clutch piston also serves as a high-clutch drum, the radial dimension of the apparatus is restricted to decrease the radial dimension of plates of the high clutch, lowering the clutch capacity, i.e., heat and torque capacities of the high clutch; PA1 2) Due to heavy weight of a member disposed inside the reverse-clutch drum, distortion of the drum is easy to occur by a centrifugal force with rotation thereof. Specifically, since, with the reverse clutch engaged, the reverse-clutch piston transmits power to the reverse-clutch drum through the piston stopper, the conventional aluminum-alloy piston is deficient in strength, requiring a material change to iron, resulting in increased weight; and PA1 3) Two splines are needed in inner surfaces of the reverse-clutch drum and the reverse-clutch piston, resulting in increased manufacturing cost. PA1 a clutch drum directly connected to the input shaft; PA1 first and second clutch hubs arranged in said clutch drum, said first and second clutch hubs being separate members, respectively; PA1 first and second clutches, each including plates engaged with an inner surface of said clutch drum, said first and second clutches transmitting, when engaged, rotation of the input shaft to said first and second clutch hubs, respectively, said first and second clutches being disposed adjacent to each other so as not to axially overlap with each other; and PA1 first and second pistons arranged in said clutch drum, said first and second pistons being axially placed on each other, said first and second pistons being movable with respect to said plates of said first and second clutches. PA1 an input shaft; PA1 a clutch drum directly connected to said input shaft; PA1 first and second clutch hubs arranged in said clutch drum, said first and second clutch hubs being separate members, respectively; PA1 first and second clutches, each including plates engaged with an inner surface of said clutch drum, said first and second clutches transmitting, when engaged, rotation of said input shaft to said first and second clutch hubs, respectively, said first and second clutches being disposed adjacent to each other so as not to axially overlap with each other; and PA1 first and second pistons arranged in said clutch drum, said first and second pistons being axially spaced relative to each other, said first and second pistons being movable with respect to said plates of said first and second clutches.
The solution of the above problems is proposed, for example, in the document entitled "Advanced Shift Control Technology on Newly-developed Automatictransaxle" published in May, 1995 by the Automotive Technical Society. Specifically, the reverse-clutch piston with piston stopper is arranged to the reverse-clutch drum on the inner-diameter side thereof so as not to rotate relative to the reverse-clutch drum. The reverse-clutch piston also serves as a high-clutch drum.
The high clutch has an input side directly connected to the input shaft through the reverse-clutch piston and the reverse-clutch drum, and an output side connected to the pinion carrier of the front planetary gear through the high-clutch hub. The reverse clutch has an output side connected to the sun gear of the front planetary gear through the reverse-clutch hub.
With this apparatus, the two pistons are axially placed on each other, obtaining reduced axial dimension of the apparatus. Further, the reverse-clutch drum, which rotates in the same way as the input shaft, is disposed at the outer side of the apparatus, enabling easy arrangement of the turbine sensor. Furthermore, only the reverse-clutch hub serves as a sun-gear connected member, so that, even when racing the engine at N range with the high clutch seizing, burst of the reverse-clutch drum can be avoided.
However, the above proposition also has the following problems:
It is, therefore, an object of the present invention to provide a hydraulic engagement apparatus for automatic transmissions that can secure required clutch capacity with no distortion of the reverse-clutch drum, nor increase in manufacturing cost and weight.